Step 1: Understand the sequence of nuclear reactions.
In the given nuclear reaction, a heavy nucleus undergoes a sequence of decay steps. The first decay is \( \gamma \) emission, which is followed by \( \alpha \)-decay, and finally, \( \beta \)-decay.
Step 2: Identify the correct order.
Thus, the correct sequence of radiation emissions is \( \alpha, \beta, \gamma \).
Final Answer:
\[
\boxed{\alpha, \beta, \gamma}
\]